1. Field of the Invention
The present invention relates to improvements in rotary pumps, and particularly to increasing the performance of rotary pumps by modifying the velocity profile upstream of the rotor.
2. Description of the Prior Art
The design procedure for most prior art rotary pumps is based on the assumption of a uniform pump inlet velocity from rotor hub to tip. Unfortunately however, the inlet velocity profile in conventional rotary pumps is not uniform. A non-uniform pump inlet velocity results, in part, from the boundary layer and in part from the cascade induced incidence (CII) effect angle. (See, for example, Scholz, Norbert, "Aerodynamics of Cascades", an English revised version AGARD 1977, pg. 211.)
The typically designed inducer leading edge hub-tip blade angle distribution may be represented by the equation:
R.multidot.tan .beta.=constant, where PA1 R=radius at a location between the hub and the tip PA1 .beta.=blade angle corresponding to R PA1 n=3Re.sup.1/12 where Re.gtoreq.3200 PA1 .sigma.=R.sub.HUB /R.sub.T, and PA1 0.8.ltoreq.K.ltoreq.1
In actual non-uniform flow, when a blade is constructed in accordance with the above equation, the tip will experience a higher incidence angle than predicted. The hub will have a much lower incidence angle than predicted. Therefore, conventional design procedures result in reduced pump suction capability and pump efficiency.